Detection of Micro-Probe Displacement Using a Shack-Hartmann Wavefront Sensor

To decrease the effort to detect micromechanical features by touch probe measuring systems, multiple touch probes composed in an array are used to measure some of these structures at the same time, owing to the alignment of many similar structures on a wafer. While usually the touch probe signal is read out electronically, in this investigation a Shack-Hartmann sensor is used to observe the reflective back plane of the micro probe array. Shack-Hartmann wave-front sensors use microlens arrays in conjunction with a CCD array. A planar wave-front that is transmitted through a microlens array and imaged on a CCD sensor will form a regular pattern of bright spots. If, however, the wave-front is distorted, the light imaged on the CCD sensor will consist of some regularly spaced spots mixed with displaced spots and missing spots. This information is used to calculate the shape of the wave-front that occurred on the microlens array.